[ENet-discuss] NAT hole punching with Enet - query on anapproach

[Mark Palkow]

Hi Martin,

We do it like Shawn described and it works fine.
The code looks like this:
sendto( host->socket, ..., ...,0,(sockaddr*)&to, toLen);

btw:
We using ENet since 1.0 for video conferencing (PlaceCam 3) there audio is
send unreliable while video is send reliable.

Regards
Mark

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-----Ursprüngliche Nachricht-----
Von: enet-discuss-bounces at cubik.org [mailto:enet-discuss-bounces at cubik.org]
Im Auftrag von Shawn Yarbrough
Gesendet: Montag, 27. April 2009 14:08
An: Discussion of the ENet library
Cc: enet-discuss at cubik.org
Betreff: Re: [ENet-discuss] NAT hole punching with Enet - query on
anapproach


You possibly might want to do your hole-punching with plain UDP packets
before you bring ENet into the connection. Because UDP has no strict notion
of a connection, you can send UDP packets one at a time in whichever
direction(s) you need to accomplish the hole punch.

Then set up an ENet connection from client to server over the same UDP port
numbers. The firewalls involved won't know the difference between the
original UDP packets and the later ENet packets.

Note I have not done this but I do know it is how UDP is supposed to work.



On Apr 27, 2009, at 4:34 AM, "M. Rijks" <enet at forge.dds.nl> wrote:

Hi all,

Another query I would appreciate your advice on. I'll be a bit lengthy to
paint the whole picture, apologies for the bloat. :)

To allow player-hosted servers and clients to connect to each other, I'm
trying to design a hole punching technique that should help both peers to
traverse firewalls and NATs. This is how I currently plan it:

1. Both the client and the game server connect to a public service (which I
call the lobby server). Since most firewalls allow packets going out to a
peer to be returned from that peer, this initial connection should pose
little problem.
2. The game server then notifies the lobby server that it is opening up a
session.
3. The client asks for a list of sessions from the lobby server.
4. The lobby server returns the public IP and port of each connected game
server.
5. The client selects the session it wishes to join from the list.

The trouble is where the remote firewall only accepts incoming connections
on that port when an outgoing connection to the client peer was already
sent. To battle this:

6. The client sends a message to the lobby server, telling it which session
it is trying to join.
7. The lobby server gives the public IP+port of the client to the game
server and tells it to fire a connection attempt to that the client
8. The client ultimately connects to the game server directly. Since the
game server made the first attempt to connect, it should have no problem to
respond.

This is where my query comes in. I only use the game server's connect
attempt towards the client to punch the hole - as soon as a (or ANY) packet
is sent through the port, the connect attempt may immediately be dropped.
Naturally, should the packet be received on the client it should, too, be
dropped - I want the client to connect to the game server and not vice
versa.

So what happens if client and game server simultaneously try to connect to
each other? Can a connect attempt be immediately dropped at the game server?
Can the incoming request at the client end, if any, be ignored? Or will I
get into some sort of communication mayhem?

Thanks in advance for any response!

Martin

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